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    <title>Document</title>
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<body>
    <input type="text">
    <button>添加</button>
    <ul></ul>
    <script>
        const url = 'http://www.liulongbin.top:3006/api/addbook';
        const inp = document.querySelector('input');
        const btn = document.querySelector('button');
        btn.addEventListener('click', function () {
           const data = {
               bookname: inp.value,
               author: 'zhenghonglian',
               publisher: '人民日报',
           }

           const xhr = new XMLHttpRequest();
           xhr.open('POST', url);

        //    xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
        //    xhr.send(Object.keys(data).map(key =>`${key}=${data[key]}`).join('&'));

           xhr.setRequestHeader('Content-Type', 'application/json');
           xhr.send(JSON.stringify(data));

           xhr.onreadystatechange = function () {
               if (xhr.readyState === 4 && xhr.status === 200) {
                   console.log(JSON.parse(xhr.responseText));
               }
           }
        })
    </script>
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